1. Field of the Invention
The present invention relates to a photographic flash device and, more particularly, to a reflector in a light emission section of a photographic flash device used in a camera.
2. Description of the Related Art
An example of a light emission section of a conventional photographic flash device is shown in FIGS. 6 and 7. As is well known, the conventional photographic flash device comprises a bar-like, straight-tube-shaped flash discharge tube 11; a reflector 12, disposed so as to cover the discharge tube 11, which reflector is formed of a reflection cap, the front side of reflector 12 being open and in the shape of a rectangle; and a diffusion plate (not shown) disposed to face the opening of the reflector 12.
The flash discharge tube 11 is formed of what is commonly called a xenon flash discharge lamp, in which tube xenon gas is sealed. A high voltage is applied to an anode 11a and a cathode 11b, which face each other, and a high trigger pulse voltage is applied to a trigger electrode thereof, so that the tube 11 emits flash light.
As shown in FIG. 6, a cross section (a longitudinal cross section) of the reflector 12 along the short side thereof is formed into a curved surface nearly semi-elliptical in shape, the front side thereof being open. As shown in FIG. 7, a plane shape of the reflector is a trapezoid or almost a trapezoid, and is formed into a transversely elongated bucket along the long side of the reflector 12. The flash discharge tube 11 is mounted so as to be positioned near the focal position of the curved surface nearly semi-elliptical in shape and along the long side of the reflector 12 in the inner surface thereof, which reflector is formed of an aluminum alloy. Therefore, when the flash discharge tube 11 emits light, the light is reflected by the inner surface of the reflector 12 and irradiated forward from a front open portion 12a having a perimeter the shape of a rectangle.
The size of the reflector 12 constructed as described above is set so that, as shown in FIG. 6, an angle between two lines 13a and 13b which connect opposing end portions of extreme edge portions of the reflector 12 and a central light emission portion of the flash discharge tube 11 is set at an angle equal to the angle of view of a photographic lens of a camera, or slightly greater than this angle. This makes it possible for almost all of the light to be irradiated within the angle of view W, thus achieving efficient illumination. For this purpose, it is preferable that the reflection surface of the inner surface of the reflector 12 be shaped to be a semi-ellipse as regards the shape of the cross section along the short side of the reflector 12. Since the flash discharge tube 11 is positioned near the focal position of the semi-ellipse of the reflector 12, regarding the light emission from the flash discharge tube 11, both the light which is emitted forward directly from the front open portion 12a and light which is reflected by the inner surface of the reflector 12 and emitted forward from the front open portion 12a can be kept within the angle of view W.
A zoom flash device in which an irradiation angle can be adjusted at will is disclosed in Japanese Laid-Open Utility Model Application Hei/2(1990)-48934. This device is designed as follows: a flash discharge tube and a reflector disposed so as to cover the flash discharge tube are disposed so as to be movable backward and forward in the direction of the optical axis behind a lens provided in a case. The flash discharge tube and the reflector are brought close to the lens to obtain a wide irradiation angle, and the flash discharge tube and the reflector are moved away from the lens to obtain a relatively narrow irradiation angle. This zoom flash device is further provided with a reflection frame having a reflection surface in such an inner surface thereof as to enclose the reflector along the inner peripheral edge of the lens, so that when the flash discharge tube and the reflector are moved away from the lens, light beams, from among the light beams which go out from the reflector, which do not directly reach the lens, are reflected by the reflection surface of the reflection frame and made to travel toward the lens.
However, the reflector of the conventional flash device shown in FIGS. 6 and 7 constructed in the above-described way has drawbacks described below. In the reflector 12, as shown in FIG. 7, light beams 13c and 13d which go beyond the angle of view W inevitably remain along the long side of the reflector 12 because of its length.
To prevent this phenomenon, it is desirable that the depth of the reflector be made great and that the distance between the front open portion 12a of the reflector and the flash discharge tube 11 be increased. However, these dimensions are automatically determined on the basis of the shape along the short side of the reflector 12. In a camera, in particular, one using a wide-angle lens, the depth of a curved surface nearly semi-elliptical in shape tends to be small, and thus light beams going out along the long side of the reflector become larger and larger. That is, in the conventional reflector shown in FIGS. 6 and 7, satisfactory light distribution can be obtained along the short side of the reflector, but light cannot be controlled along the long side thereof and thus a large number of light beams go beyond the angle of view W. The dimension of the depth of the reflector depends upon the curved surface of the cross section along the short side of the reflector 12. The depth becomes small when an attempt is made to obtain light distribution for a wide-angle lens, and therefore light is wasted more along the long side of the reflector than the short side thereof.
No mention as to light wasted along the long side of the reflector is made in Japanese Laid-Open Utility Model Application Hei/2(1990)-48934 disclosing the zoom reflector device.